Co2 recovery unit and co2 recovery method

ABSTRACT

A CO 2  recovery unit includes an absorber that reduces CO 2  in flue gas ( 101 ) discharged from a combustion facility ( 50 ) by absorbing CO 2  by an absorbent, a regenerator that heats the absorbent having absorbed CO 2  to emit CO 2 , and regenerates and supplies the absorbent to the absorber, and a regenerating heater that uses steam ( 106 ) supplied from the combustion facility ( 50 ) for heating the absorbent in the regenerator and returns heated condensed water ( 106   a ) to the combustion facility ( 50 ). The CO 2  recovery unit further includes a condensed water/flue gas heat exchanger ( 57 ) that heats the condensed water ( 106   a ) to be returned from the regenerating heater to the combustion facility ( 50 ) by heat-exchanging the condensed water ( 106   a ) with the flue gas ( 101 ) in a flue gas duct ( 51 ) in the combustion facility ( 50 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 13/580,469, filed Aug.22, 2012, which is a 371 of PCT/JP2011/050285 filed Jan. 11, 2011, whichclaims priority to JP 2010-037790, filed Feb. 23, 2010, the entirecontents of which is incorporated herein by reference.

FIELD

The present invention relates to a CO₂ recovery unit and a CO₂ recoverymethod for promoting energy savings.

BACKGROUND

The greenhouse effect by CO₂ (carbon dioxide) has been pointed out asone of the causes of the global warming, and there is an urgent need totake measures against it for protecting the global environment on aglobal scale. The generation source of CO₂ ranges over all humanactivities that burn fossil fuel, and thus demands for emissionlimitation on CO₂ are further increasing. Along with this trend,targeting for power generating facilities such as a thermal power plantthat uses a large amount of fossil fuel, a method of reducing andrecovering CO₂ in flue gas by bringing flue gas from a boiler intocontact with an amine absorbent such as an amine compound solution hasbeen intensively studied.

As a CO₂ recovery unit that recovers CO₂ from flue gas from a boiler orthe like by using an absorbent, there has been known a CO₂ recovery unitthat reduces CO₂ in flue gas by bringing flue gas into contact with aCO₂ absorbent in an absorber, heats the absorbent that has absorbed CO₂in a regenerator so as to emit CO₂ and to regenerate the absorbent, andthen returns the absorbent to the absorber and reuses the absorbent(see, for example, Patent Literature 1).

To separate and recover CO₂ in the regenerator, the absorbent needs tobe heated in a reboiler, and thus steam of a predetermined pressure forheating needs to be supplied. Conventionally, it has been proposed toregenerate the steam by using a part of steam generated in a combustionfacility such as a boiler in a power plant (see, for example, PatentLiterature 2).

Steam supplied to the regenerator becomes condensed water after heatingthe absorbent that has absorbed CO₂, and is returned to a combustionfacility and heated again.

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Patent Application Laid-open No. H5-245339

Patent Literature 2: Japanese Utility Model Laid-open Publication No.H3-193116

SUMMARY Technical Problem

As described above, a CO₂ recovery unit is installed while being addedto a combustion facility, and consumes thermal energy of the combustionfacility. Therefore, there is a problem that energy efficiency of thecombustion facility is lowered. For example, in the case of a powergenerating facility, thermal energy of the power generating facility isconsumed, thereby lowering a power output thereof.

The present invention has been achieved in view of the above problems,and an object of the present invention is to provide a CO₂ recovery unitand a CO₂ recovery method that can improve energy efficiency.

Solution to Problem

According to an aspect of the present invention, an CO₂ recovery unitincludes: an absorber that reduces CO₂ in flue gas discharged from acombustion facility by absorbing CO₂ by an absorbent; a regenerator thatheats the absorbent having absorbed CO₂ to emit CO₂, and regenerates andsupplies the absorbent to the absorber; a regenerating heater that usessteam supplied from the combustion facility for heating the absorbent inthe regenerator and returns heated condensed water to the combustionfacility; and a condensed water/flue gas heat exchanger that heatscondensed water to be returned from the regenerating heater to thecombustion facility by heat-exchanging the condensed water with flue gasin a flue gas duct in the combustion facility.

According to the CO₂ recovery unit, because condensed water returnedfrom the regenerating heater to the combustion facility by the condensedwater/flue gas heat exchanger is preheated, consumption energy in thecombustion facility can be reduced, thereby enabling to improve energyefficiency in a plant in which the CO₂ recovery unit is applied.

Advantageously, in the CO₂ recovery unit, a condensed water/flue gasheat exchanging line for heat-exchanging between condensed water andflue gas is provided in middle of a condensed water line for returningcondensed water from the regenerating heater to the combustion facility,and a bypass line for directly connecting the condensed water linewithout via the condensed water/flue gas heat exchanging line isprovided.

According to the CO₂ recovery unit, for example, when there is a loadvariation in at least one of a plant in which the CO₂ recovery unit isapplied and the CO₂ recovery unit, a heat exchange amount betweencondensed water and flue gas in the condensed water/flue gas heatexchanger can be adjusted by the bypass line. Accordingly, a stableoperation can be performed even at the time of the load variation.

Advantageously, the CO₂ recovery unit further includes: a circulatingwater/flue gas heat exchanger that performs heat exchange betweencirculating water and flue gas in a flue gas duct in the combustionfacility, at a downstream of flue gas of the condensed water/flue gasheat exchanger; and a circulating water/absorbent heat exchanger thatperforms heat exchange between an absorbent having absorbed CO₂ in theabsorber and the circulating water before the absorbent reaches theregenerator.

According to the CO₂ recovery unit, the absorbent is heated beforereaching the regenerator by using heat of flue gas. Therefore, an amountof steam required in the regenerating heater for heating the absorbentcan be reduced. Accordingly, consumption energy in the combustionfacility required for recovering CO₂ can be reduced, thereby enabling toimprove energy efficiency in a plant in which the CO₂ recovery unit isapplied.

Advantageously, the CO₂ recovery unit further includes an air preheaterthat preheats combustion air before reaching the combustion facility bywaste heat discharged in a process of recovering CO₂.

According to the CO₂ recovery unit, combustion air is preheated by usingwaste heat discharged in the process of recovering CO₂. Therefore, thetemperature of flue gas discharged from the combustion facility rises,thereby increasing a heat exchange amount in the condensed water/fluegas heat exchanger. As a result, the temperature of condensed waterreturned from the regenerating heater to the combustion facility rises,thereby enabling to reduce consumption energy in the combustion facilityrequired for recovering CO₂, and to improve energy efficiency in a plantin which the CO₂ recovery unit is applied.

Advantageously, the CO₂ recovery unit further includes an air preheaterthat preheats combustion air before reaching the combustion facility bythe condensed water before reaching the condensed water/flue gas heatexchanger.

According to the CO₂ recovery unit, combustion air is preheated by usingcondensed water before reaching the condensed water/flue gas heatexchanger. Therefore, the temperature of flue gas discharged from thecombustion facility rises, thereby increasing the heat exchange amountin the condensed water/flue gas heat exchanger. As a result, thetemperature of condensed water returned from the regenerating heater tothe combustion facility rises, thereby enabling to reduce consumptionenergy in the combustion facility required for recovering CO₂, and toimprove energy efficiency in a plant in which the CO₂ recovery unit isapplied.

According to another aspect of the present invention, an CO₂ recoverymethod includes: a CO₂ absorbing step of reducing CO₂ in flue gasdischarged from a combustion facility by absorbing CO₂ by an absorbent;an absorbent regenerating step of heating the absorbent having absorbedCO₂ to emit CO₂, and regenerating and supplying the absorbent to the CO₂absorbing step; a regeneration heating step of using steam supplied fromthe combustion facility for heating the absorbent at the absorbentregenerating step and returning heated condensed water to the combustionfacility, and reusing the regenerated absorbent at the CO₂ absorbingstep; and a condensed water/flue gas heat exchanging step of heatingcondensed water to be returned to the combustion facility byheat-exchanging the condensed water with flue gas in a flue gas duct inthe combustion facility.

According to the CO₂ recovery method, because condensed water returnedfrom the regeneration heating step to the combustion facility by thecondensed water/flue gas heat exchanging step is preheated, consumptionenergy in the combustion facility can be reduced, thereby enabling toimprove energy efficiency in a plant in which the CO₂ recovery unit isapplied.

Advantageously, the CO₂ recovery unit further includes a non-heatexchanging step of returning condensed water to the combustion facilitywithout via the condensed water/flue gas heat exchanging step.

According to the CO₂ recovery method, for example, when there is a loadvariation in at least one of a plant in which the CO₂ recovery unit isapplied and the CO₂ recovery unit, a heat exchange amount betweencondensed water and flue gas at the condensed water/flue gas heatexchanging step can be adjusted by the non-heat exchanging step.Accordingly, a stable operation can be performed even at the time of theload variation.

Advantageously, the CO₂ recovery unit further includes a circulatingwater/flue gas heat exchanging step of performing heat exchange betweencirculating water and flue gas in a flue gas duct in the combustionfacility, at a downstream of flue gas of the condensed water/flue gasheat exchanging step; and a circulating water/absorbent heat exchangingstep of performing heat exchange between an absorbent having absorbedCO₂ at the CO₂ absorbing step and the circulating water beforeperforming the absorbent regenerating step.

According to the CO₂ recovery method, the absorbent is heated beforeperforming the absorbent regenerating step by using heat of flue gas.Therefore, an amount of steam required for the regeneration heating stepfor heating the absorbent can be reduced. Accordingly, consumptionenergy in the combustion facility required for recovering CO₂ can bereduced, thereby enabling to improve energy efficiency in a plant inwhich the CO₂ recovery unit is applied.

Advantageously, the CO₂ recovery unit further includes an air preheatingstep of preheating combustion air before reaching the combustionfacility by waste heat discharged in a process of recovering CO₂.

According to the CO₂ recovery method, combustion air is preheated byusing waste heat discharged in the process of recovering CO₂. Therefore,the temperature of flue gas discharged from the combustion facilityrises, thereby increasing a heat exchange amount at the condensedwater/flue gas heat exchanging step. As a result, the temperature ofcondensed water returned from the regenerating heater to the combustionfacility rises, thereby enabling to reduce consumption energy in thecombustion facility required for recovering CO₂, and to improve energyefficiency in a plant in which the CO₂ recovery unit is applied.

Advantageously, the CO₂ recovery unit further includes an air preheatingstep of preheating combustion air before reaching the combustionfacility by the condensed water before performing the condensedwater/flue gas heat exchanging step.

According to the CO₂ recovery method, combustion air is preheated byusing condensed water before reaching the condensed water/flue gas heatexchanging step. Therefore, the temperature of flue gas discharged fromthe combustion facility rises, thereby increasing the heat exchangeamount at the condensed water/flue gas heat exchanging step. As aresult, the temperature of condensed water returned from theregenerating heater to the combustion facility rises, thereby enablingto reduce consumption energy in the combustion facility required forrecovering CO₂, and to improve energy efficiency in a plant in which theCO₂ recovery unit is applied.

Advantageous Effects of Invention

According to the present invention, consumption energy in a combustionfacility is reduced and energy efficiency thereof can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a plant in which a CO₂ recovery unitaccording to a first embodiment of the present invention is applied.

FIG. 2 is a schematic diagram of the CO₂ recovery unit according to thefirst embodiment of the present invention.

FIG. 3 is a schematic diagram of a plant in which a CO₂ recovery unitaccording to another mode of the first embodiment of the presentinvention is applied.

FIG. 4 is a schematic diagram of a plant in which a CO₂ recovery unitaccording to a second embodiment of the present invention is applied.

FIG. 5 is a schematic diagram of the CO₂ recovery unit according to thesecond embodiment of the present invention.

FIG. 6 is a schematic diagram of a plant in which a CO₂ recovery unitaccording to a third embodiment of the present invention is applied.

FIG. 7 is a schematic diagram of a plant in which a CO₂ recovery unitaccording to a fourth embodiment of the present invention is applied.

FIG. 8 depicts a power output reduction rate of a thermal powergenerating facility according to Examples of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be explained below in detailwith reference to the accompanying drawings. The present invention isnot limited to the embodiments. In addition, constituent elements in theembodiments include those that can be easily replaced or assumed bypersons skilled in the art, or that are substantially equivalent.

First Embodiment

A first embodiment of the present invention is explained with referenceto the drawings. FIG. 1 is a schematic diagram of a plant in which a CO₂recovery unit according to the first embodiment is applied. FIG. 2 is aschematic diagram of the CO₂ recovery unit according to the firstembodiment.

As shown in FIG. 1, a plant 5, for example, a power generation plantmainly includes a boiler that heats water in a sealed vessel by thethermal energy acquired by burning fuel, thereby acquiringhigh-temperature and high-pressure superheated steam, a combustionfacility 50 including various turbines that acquire rotative power bysuperheated steam from the boiler, and a power generator (not shown)that generates power by the rotative power of a steam turbine. Althoughnot shown in FIG. 1, the turbine includes a high pressure turbine, anintermediate pressure turbine, and a low pressure turbine. The plant 5further includes a desulfurizer 52 that reduces sulfur content(including a sulfur compound) contained in flue gas 101 in a flue gasduct 51 for the passage of the flue gas 101 discharged from the boilerin the combustion facility 50, and a CO₂ recovery unit 53 that reducesCO₂ (carbon dioxide) contained in the flue gas 101 discharged from theboiler in the combustion facility 50. That is, a power generation plantas the plant 5 generates power by superheated steam from the boiler inthe combustion facility 50, and discharges from a stack 54 emission gas101 a, from which sulfur content and CO₂ discharged from the boiler inthe combustion facility 50 are reduced.

In this type of plant 5, the boiler in the combustion facility 50 isprovided with an air/flue gas heat exchanger 55. The air/flue gas heatexchanger 55 is provided while bridging an air line 56 that suppliescombustion air 102 to the boiler in the combustion facility 50 and theflue gas duct 51, and performs heat exchange between the flue gas 101discharged from the boiler and the combustion air 102 supplied to theboiler. The air/flue gas heat exchanger 55 improves the thermalefficiency of the boiler by preheating the combustion air 102 to theboiler.

As shown in FIG. 2, the CO₂ recovery unit 53 includes a cooling column 1that cools the flue gas 101 discharged from the boiler in the combustionfacility 50 by cooling water 103, an absorber 2 that causes a leansolution 104 a of an absorbent 104, which is an aqueous solution of anamine compound that absorbs CO₂, to be brought into countercurrentcontact with the flue gas 101 to absorb CO₂ in the flue gas 101 by theabsorbent 104 and discharges the emission gas 101 a from which CO₂ isreduced, and a regenerator 3 that emits CO₂ from a rich solution 104 bof the absorbent 104 having absorbed CO₂ to regenerate it to the leansolution 104 a, and returns the lean solution 104 a to the absorber 2.

In the cooling column 1, the flue gas 101 containing CO₂ is boosted by aflue gas blower (not shown) and fed into the cooling column 1, and isbrought into countercurrent contact with the cooling water 103, therebycooling the flue gas 101.

The cooling water 103 is accumulated in a lower portion of the coolingcolumn 1, pressure-fed by a cooling-water circulating pump 1 a, andsupplied to an upper portion of the cooling column 1 through a coolingwater line 1 b. The cooling water 103 is then brought intocountercurrent contact with the flue gas 101 moving upward at a positionof a packed bed 1 d provided in a process leading to the lower portionof the cooling column 1, while flowing down from a nozzle 1 c providedin the upper portion of the cooling column 1. Furthermore, a cooler 1 eis provided in the cooling water line 1 b, and by cooling the coolingwater 103 to a temperature lower than that of the flue gas 101, a partof moisture in the flue gas 101 condenses in the cooling column 1 tobecome condensed water. The flue gas 101 cooled in the cooling column 1is discharged from a top portion of the cooling column 1 through a fluegas line if and supplied to the absorber 2.

The absorber 2 has a CO₂ absorbing unit 21 in a lower portion thereof,and a water-washing unit 22 in an upper portion thereof. The CO₂absorbing unit 21 brings the flue gas 101 supplied from the coolingcolumn 1 into countercurrent contact with the lean solution 104 a of theabsorbent 104, so that CO₂ in the flue gas 101 is absorbed by theabsorbent 104 and reduced (CO₂ absorbing step).

The lean solution 104 a of the absorbent 104 is supplied from theregenerator 3, and brought into countercurrent contact with the flue gas101 moving upward at a position of a packed bed 21 b provided in aprocess leading to the lower portion of the absorber 2, while flowingdown from a nozzle 21 a, to become the rich solution 104 b havingabsorbed CO₂, and then accumulated at a bottom portion of the absorber2. The rich solution 104 b of the absorbent 104 accumulated at thebottom portion of the absorber 2 is then pressure-fed by a rich-solutiondischarge pump 21 c positioned outside of the absorber 2, and suppliedto the regenerator 3 through a rich solution line 21 d. Furthermore, inthe process of being supplied to the regenerator 3 through the richsolution line 21 d, the rich solution 104 b of the absorbent 104 isheat-exchanged with the lean solution 104 a of the absorbent 104 in theprocess of being supplied to the absorber 2 through a lean solution line31 d described later, by a rich/lean heat exchanger 4.

The water-washing unit 22 brings the emission gas 101 a, from which CO₂is reduced by the CO₂ absorbing unit 21, into countercurrent contactwith wash water 105 to reduce the amine compound entrained with theemission gas 101 a by the wash water 105, and discharges the emissiongas 101 a, from which the amine compound is reduced, to outside of theabsorber 2.

The wash water 105 is brought into countercurrent contact with theemission gas 101 a moving upward at a position of a packed bed 22 bprovided in a process leading to the lower part of the absorber 2, whileflowing down from a nozzle 22 a, and is accumulated in a water receiver22 c. The wash water 105 accumulated in the water receiver 22 c is thenpressure-fed by a wash-water discharge pump 22 d positioned outside ofthe absorber 2, cooled by a cooler 22 f, while being circulated througha wash water line 22 e, and caused to flow down from the nozzle 22 aagain.

The regenerator 3 has an absorbent regenerating unit 31 in a lower halfthereof. The absorbent regenerating unit 31 recovers CO₂ from the richsolution 104 b of the absorbent 104 and regenerates it as the leansolution 104 a, thereby emitting CO₂ from the absorbent 104 havingabsorbed CO₂ (absorbent regenerating step).

The rich solution 104 b of the absorbent 104 is supplied through therich solution line 21 d of the CO₂ absorbing unit 21 in the absorber 2,and caused to flow down from a nozzle 31 a. The rich solution 104 b thenbecomes the lean solution 104 a, from which almost all CO₂ has beenemitted, due to an endothermic reaction by a regenerating heater 32connected to a lower portion of the regenerator 3, while passing througha lower-portion packed bed 31 b provided in a process leading to thelower portion of the regenerator 3, and accumulated at a bottom portionof the regenerator 3. Subsequently, in a process of being pressure-fedby a lean-solution discharge pump 31 c positioned outside of theregenerator 3, and supplied to the absorber 2 through the lean solutionline 31 d, the lean solution 104 a accumulated at the lower portion ofthe regenerator 3 is heat-exchanged with the rich solution 104 b in theprocess of being supplied to the regenerator 3 through the rich solutionline 21 d by the rich/lean heat exchanger 4, and cooled by a cooler 31e.

Meanwhile, the emitted CO₂ moves upward in the regenerator 3, passesthrough an upper-portion packed bed 31 f, and discharged from a topportion of the regenerator 3. At this time, because moisture iscontained in CO₂, by cooling CO₂ in a cooler 33 b, the moisturecontained in CO₂ is condensed, and the condensed water and CO₂ areseparated by a CO₂ separator 33 c. High-purity CO₂ separated fromcondensed water is emitted from a CO₂ emission line 33 d to outside of asystem of a CO₂ recovery process, and used or dispensed with insubsequent steps. The condensed water is transported by a condensedwater pump 33 e, a part of which is supplied from a nozzle 33 g at a toppart of the regenerator 3 into the regenerator 3, through a regeneratorreflux-water line 33 f.

The regenerating heater 32 heats the absorbent 104 accumulated at thebottom portion of the regenerator 3 by steam 106, in a circulatingprocess for returning the absorbent 104 to the bottom portion of theregenerator 3, while extracting the absorbent 104 to outside of theregenerator 3 via a heating line 32 a. The steam 106 supplied to theregenerating heater 32 by a steam extracting line 32 b is condensed tobecome condensed water 106 a after heating the absorbent 104, anddischarged via a condensed water line 32 c (regeneration heating step).

Furthermore, the absorbent regenerating unit 31 is provided with a leansolution/condensed water heat recovery unit 34. The leansolution/condensed water heat recovery unit 34 performs heat exchangeamong the extracted absorbent 104 and the lean solution 104 a of theabsorbent 104 in a process of being supplied to the absorber 2 throughthe lean solution line 31 d and the condensed water 106 a in a processof being discharged through the condensed water line 32 c, in thecirculating process for returning the absorbent 104 in the process ofbeing regenerated in the absorbent regenerating unit 31 to theregenerator 3, while extracting the absorbent 104 to outside of theregenerator 3.

In the CO₂ recovery unit 53 described above, in the regenerating heater32 (regeneration heating step), as shown in FIG. 1, the steam 106supplied to the regenerating heater 32 is extracted from the combustionfacility 50 in the plant 5 via the steam extracting line 32 b (the signA in FIG. 1 and FIG. 2). Furthermore, in the CO₂ recovery unit 53, thecondensed water 106 a after being used for heating the absorbent 104 inthe regenerating heater 32 is returned to the boiler in the combustionfacility 50 via the condensed water line 32 c (the sign B in FIG. 1 andFIG. 2). The condensed water 106 a to be returned to the boiler in thecombustion facility 50 from the regenerating heater 32 in the CO₂recovery unit 53 via the condensed water line 32 c is returned to theboiler in the combustion facility 50, while dissolved oxygen is removedby a deaerator (not shown).

As shown in FIG. 1, a condensed water/flue gas heat exchanging line 57 ais put in the condensed water line 32 c. The condensed water/flue gasheat exchanging line 57 a is extended to the flue gas duct 51 disposedbetween the air/flue gas heat exchanger 55 and the desulfurizer 52 toform a condensed water/flue gas heat exchanger 57 (condensed water/fluegas heat exchanging step) that heats the condensed water 106 a to bereturned from the regenerating heater 32 to the combustion facility 50by heat-exchanging the condensed water 106 a with the flue gas 101 inthe flue gas duct 51.

As described above, the CO₂ recovery unit 53 according to the firstembodiment includes the absorber 2 that reduces CO₂ in the flue gas 101discharged from the combustion facility 50 by absorbing CO₂ by the leansolution 104 a of the absorbent 104, the regenerator 3 that heats therich solution 104 b of the absorbent 104 having absorbed CO₂ to emitCO₂, and regenerates and supplies the absorbent to the absorber 2, andthe regenerating heater 32 that uses the steam 106 supplied from thecombustion facility 50 for heating the absorbent 104 in the regenerator3 and returns the heated condensed water 106 a to the combustionfacility 50. The CO₂ recovery unit further includes the condensedwater/flue gas heat exchanger 57 that heats the condensed water 106 a tobe returned from the regenerating heater 32 to the combustion facility50 by heat-exchanging the condensed water 106 a with the flue gas 101 inthe flue gas duct 51 in the combustion facility 50.

According to the CO₂ recovery unit 53, because the condensed water 106 ato be returned from the regenerating heater 32 to the combustionfacility 50 is preheated by the condensed water/flue gas heat exchanger57, consumption energy in the combustion facility 50 can be reduced,thereby enabling to improve energy efficiency in the plant 5 in whichthe CO₂ recovery unit 53 is applied.

FIG. 3 depicts another mode of the CO₂ recovery unit 53 according to thefirst embodiment. As shown in FIG. 3, a bypass line 57 b that directlyconnects the condensed water line 32 c without via the condensedwater/flue gas heat exchanging line 57 a is provided in the condensedwater line 32 c for returning the condensed water 106 a from theregenerating heater 32 to the combustion facility 50. Furthermore, anon-off valve 57 c is provided on an upstream side of the condensedwater/flue gas heat exchanging line 57 a for feeding the condensed water106 a to the condensed water/flue gas heat exchanger 57. Further, anon-off valve 57 d is provided in the bypass line 57 b.

When heat exchange between the condensed water 106 a and the flue gas101 is performed in the condensed water/flue gas heat exchanger 57, theon-off valve 57 c is opened, and the on-off valve 57 d is closed. Withthis configuration, the condensed water 106 a in a process of beingreturned to the combustion facility 50 via the condensed water line 32 cpasses through the condensed water/flue gas heat exchanging line 57 a.Therefore, heat exchange between the condensed water 106 a and the fluegas 101 is performed in the condensed water/flue gas heat exchanger 57.

On the other hand, when heat exchange between the condensed water 106 aand the flue gas 101 is not performed in the condensed water/flue gasheat exchanger 57, the on-off valve 57 c is closed, and the on-off valve57 d is opened. With this configuration, the condensed water 106 a inthe process of being returned to the combustion facility 50 via thecondensed water line 32 c is returned to the combustion facility 50without via the condensed water/flue gas heat exchanging line 57 a.Therefore, heat exchange between the condensed water 106 a and the fluegas 101 is not performed in the condensed water/flue gas heat exchanger57 (non-heat exchanging step).

As described above, in the CO₂ recovery unit 53 according to the firstembodiment, the condensed water/flue gas heat exchanging line 57 a forperforming heat exchange between the condensed water 106 a and the fluegas 101 is provided in the middle of the condensed water line 32 c forreturning the condensed water 106 a from the regenerating heater 32 tothe combustion facility 50, and the bypass line 57 b for directlyconnecting the condensed water line 32 c without via the condensedwater/flue gas heat exchanging line 57 a is provided.

According to the CO₂ recovery unit 53, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount between the condensed water 106 a and the fluegas 101 in the condensed water/flue gas heat exchanger 57 can beadjusted by the bypass line 57 b. Accordingly, a stable operation can beperformed even at the time of the load variation.

A CO₂ recovery method according to the first embodiment includes a CO₂absorbing step of reducing CO₂ in the flue gas 101 discharged from thecombustion facility 50 by absorbing CO₂ by the rich solution 104 b ofthe absorbent 104, an absorbent regenerating step of heating the richsolution 104 b of the absorbent 104 having absorbed CO₂ to emit CO₂, andregenerating and supplying the absorbent to the CO₂ absorbing step, anda regeneration heating step of using the steam 106 supplied from thecombustion facility 50 for heating the absorbent 104 at the absorbentregenerating step and returning the heated condensed water 106 a to thecombustion facility 50. The CO₂ recovery method further includes acondensed water/flue gas heat exchanging step of heating the condensedwater 106 a to be returned to the combustion facility 50 byheat-exchanging the condensed water 106 a with the flue gas 101 in theflue gas duct 51 in the combustion facility 50.

According to the CO₂ recovery method, because the condensed water 106 ato be returned from the regeneration heating step to the combustionfacility 50 is preheated by the condensed water/flue gas heat exchangingstep, consumption energy in the combustion facility 50 can be reduced,thereby enabling to improve energy efficiency in the plant 5 in whichthe CO₂ recovery method is applied.

Furthermore, the CO₂ recovery method according to the first embodimentincludes a non-heat exchanging step of returning the condensed water 106a to the combustion facility 50 without via the condensed water/flue gasheat exchanging step.

According to the CO₂ recovery method, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount between the condensed water 106 a and the fluegas 101 at the condensed water/flue gas heat exchanging step can beadjusted by the non-heat exchanging step. Accordingly, a stableoperation can be performed even at the time of the load variation.

Second Embodiment

A second embodiment of the present invention is explained with referenceto the drawings. FIG. 4 is a schematic diagram of a plant in which a CO₂recovery unit according to a second embodiment is applied, and FIG. 5 isa schematic diagram of the CO₂ recovery unit according to the secondembodiment.

The CO₂ recovery unit 53 according to the present embodiment includesthe condensed water/flue gas heat exchanger 57 (in a CO₂ recoverymethod, condensed water/flue gas heat exchanging step), similarity tothe CO₂ recovery unit 53 according to the first embodiment. The CO₂recovery unit 53 further includes a circulating water/flue gas heatexchanger 58 a (in the CO₂ recovery method, circulating water/flue gasheat exchanging step) and a circulating water/absorbent heat exchanger58 b (in the CO₂ recovery method, circulating water/absorbent heatexchanging step). Therefore, in the second embodiment, a configurationrelated to the circulating water/flue gas heat exchanger 58 a (in theCO₂ recovery method, circulating water/flue gas heat exchanging step)and the circulating water/absorbent heat exchanger 58 b (in the CO₂recovery method, circulating water/absorbent heat exchanging step) isexplained, and elements equivalent to those in the first embodimentdescribed above are denoted by like reference signs and explanationsthereof will be omitted.

As shown in FIG. 4, the circulating water/flue gas heat exchanger 58 ais provided in the flue gas duct 51 in a downstream of the flue gas 101of the condensed water/flue gas heat exchanger 57. More specifically,the circulating water/flue gas heat exchanger 58 a is provided betweenthe condensed water/flue gas heat exchanger 57 and the desulfurizer 52in the flue gas duct 51. The circulating water/flue gas heat exchanger58 a is supplied with circulating water 107 by a circulating water line58 c.

As shown in FIG. 5, the circulating water/absorbent heat exchanger 58 bis provided in the rich solution line 21 d for supplying the richsolution 104 b of the absorbent 104 having absorbed CO₂ in the absorber2 to the regenerator 3. More specifically, the circulatingwater/absorbent heat exchanger 58 b is provided between the rich/leanheat exchanger 4 and the regenerator 3 in the rich solution line 21 d.The circulating water 107 is supplied to the circulating water/absorbentheat exchanger 58 b by the circulating water line 58 c. That is, thecirculating water 107 is circulated by the circulating water line 58 cthrough the circulating water/flue gas heat exchanger 58 a and thecirculating water/absorbent heat exchanger 58 b.

Meanwhile, in the circulating water/flue gas heat exchanger 58 a(circulating water/flue gas heat exchanging step), the circulating water107 circulated by the circulating water line 58 c (the signs C and D inFIGS. 4 and 5) is heated by-heat exchanging the circulating water 107with the flue gas 101 in the flue gas duct 51 in the combustion facility50. Furthermore, in the circulating water/absorbent heat exchanger 58 b(circulating water/absorbent heat exchanging step), the rich solution104 b of the absorbent 104 having absorbed CO₂ in the absorber 2 isheated by heat-exchanging the rich solution 104 b with the circulatingwater 107 circulated by the circulating water line 58 c (the signs C andD in FIGS. 4 and 5).

As described above, the CO₂ recovery unit 53 according to the presentembodiment includes the circulating water/flue gas heat exchanger 58 athat heats the circulating water 107 by heat-exchanging it with the fluegas 101 in the flue gas duct 51 in the combustion facility 50 in thedownstream of the flue gas 101 of the condensed water/flue gas heatexchanger 57, and the circulating water/absorbent heat exchanger 58 bthat heats the rich solution 104 b of the absorbent 104 having absorbedCO₂ in the absorber 2 by heat-exchanging the rich solution 104 b withthe circulating water 107 before reaching the regenerator 3.

According to the CO₂ recovery unit 53, the rich solution 104 b of theabsorbent 104 is heated before reaching the regenerator 3 by using theheat of the flue gas 101. Therefore, an amount of steam required by theregenerating heater 32 for heating the rich solution 104 b of theabsorbent 104 can be reduced, and thus consumption energy in thecombustion facility 50 required for recovering CO₂ can be reduced,thereby enabling to improve energy efficiency in the plant 5 in whichthe CO₂ recovery unit 53 is applied.

As shown in FIG. 4, in the CO₂ recovery unit 53 according to the secondembodiment, an on-off valve 58 d can be provided in the circulatingwater line 58 c for circulating the circulating water 107. When theon-off valve 58 d is opened, the circulating water 107 is circulated,thereby performing heat exchange between the circulating water 107 andthe flue gas 101, and between the rich solution 104 b of the absorbent104 and the circulating water 107. On the other hand, when the on-offvalve 58 d is closed, the circulating water 107 is not circulated.Therefore, the circulating water 107 and the flue gas 101 are notheat-exchanged, and the rich solution 104 b of the absorbent 104 and thecirculating water 107 are not heat-exchanged.

According to the CO₂ recovery unit 53, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount in the circulating water/flue gas heatexchanger 58 a and the circulating water/absorbent heat exchanger 58 bcan be adjusted by operating the on-off valve 58 d. Accordingly, astable operation can be performed even at the time of the loadvariation.

The CO₂ recovery method according to the second embodiment includes acirculating water/flue gas heat exchanging step of heating thecirculating water 107 by heat-exchanging it with the flue gas 101 in theflue gas duct 51 in the combustion facility 50 in the downstream of theflue gas 101 at the condensed water/flue gas heat exchanging step, and acirculating water/absorbent heat exchanging step of heating the richsolution 104 b of the absorbent 104 having absorbed CO₂ at a CO₂absorbing step by heat-exchanging the rich solution 104 b with thecirculating water 107 before performing an absorbent regenerating step.

According to the CO₂ recovery method, the rich solution 104 b of theabsorbent 104 is heated by using the heat of the flue gas 101 beforeperforming the absorbent regenerating step. Therefore, an amount ofsteam required by a regeneration heating step for heating the richsolution 104 b of the absorbent 104 can be reduced, and thus consumptionenergy in the combustion facility 50 required for recovering CO₂ can bereduced, thereby enabling to improve energy efficiency in the plant 5 inwhich the CO₂ recovery method is applied.

As shown in FIG. 4, the CO₂ recovery method according to the secondembodiment further includes a non-heat exchanging step of stopping theheat exchange at the circulating water/flue gas heat exchanging step andthe circulating water/absorbent heat exchanging step by closing theon-off valve 58 d.

According to the CO₂ recovery method, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount at the circulating water/flue gas heatexchanging step and the circulating water/absorbent heat exchanging stepcan be adjusted by operating the on-off valve 58 d. Accordingly, astable operation can be performed even at the time of the loadvariation.

In FIG. 4, which explains the present embodiment, a configurationincluding the circulating water/flue gas heat exchanger 58 a(circulating water/flue gas heat exchanging step) and the circulatingwater/absorbent heat exchanger 58 b (circulating water/absorbent heatexchanging step) is shown with respect to the configuration shown inFIG. 3, which explains the first embodiment. However, the circulatingwater/flue gas heat exchanger 58 a (circulating water/flue gas heatexchanging step) and the circulating water/absorbent heat exchanger 58 b(circulating water/absorbent heat exchanging step) can be provided inthe configuration shown in FIG. 1, which explains the first embodiment.

Third Embodiment

A third embodiment of the present invention is explained with referenceto the drawings. FIG. 6 is a schematic diagram of a plant in which a CO₂recovery unit according to the third embodiment is applied.

The CO₂ recovery unit 53 according to the present embodiment includesthe condensed water/flue gas heat exchanger 57 (in a CO₂ recoverymethod, condensed water/flue gas heat exchanging step), similarity tothe CO₂ recovery unit 53 according to the first embodiment. The CO₂recovery unit 53 further includes an air preheater 59 (in the CO₂recovery method, air preheating step). Therefore, in the thirdembodiment, a configuration of the air preheater 59 (in the CO₂ recoverymethod, air preheating step) is explained, and elements equivalent tothose in the first embodiment described above are denoted by likereference signs and explanations thereof will be omitted.

As shown in FIG. 6, the air preheater 59 has a heat discharge line 59 a.The heat discharge line 59 a is provided to circulate a heat medium 108such as circulating water between the air line 56 in an upstream of airof the air/flue gas heat exchanger 55 and a cooler that discharges heatin a process of recovering CO₂ in the CO₂ recovery unit 53. As shown inFIG. 2 (or in FIG. 5), the cooler that discharges waste heat in theprocess of recovering CO₂ in the CO₂ recovery unit 53 includes at leastone of the cooler 1 e provided in the cooling water line 1 b of thecooling column 1, the cooler 22 f provided in the wash water line 22 eof the absorber 2, the cooler 31 e provided in the lean solution line 31d extending from the regenerator 3 to the absorber 2, and the cooler 33b provided in a CO₂ emission line 33 a of a CO₂ recovering unit 33. Thatis, the heat medium 108 is circulated by the waste heat line 59 athrough the air line 56 and the coolers 1 e, 22 f, 31 e, and 33 b.

Meanwhile, in the air preheater 59 (air preheating step), the combustionair 102 in the air line 56 is preheated by heat-exchanging thecombustion air 102 with the heat medium 108 circulating through thewaste heat line 59 a (the signs E and F in FIG. 2 (in FIG. 5) and FIG.6).

As described above, the CO₂ recovery unit 53 according to the thirdembodiment includes the air preheater 59 that preheats the combustionair 102 before reaching the combustion facility 50 by waste heatdischarged in the process of recovering CO₂.

According to the CO₂ recovery unit 53, the combustion air 102 ispreheated by using waste heat discharged in the process of recoveringCO₂. Therefore, the temperature of the flue gas 101 discharged from theboiler in the combustion facility 50 rises, thereby increasing the heatexchange amount in the condensed water/flue gas heat exchanger 57. As aresult, the temperature of the condensed water 106 a returned from theregenerating heater 32 to the combustion facility 50 rises, therebyenabling to reduce consumption energy in the combustion facility 50required for recovering CO₂, and to improve energy efficiency in theplant 5 in which the CO₂ recovery unit 53 is applied.

As shown in FIG. 6, in the CO₂ recovery unit 53 according to the thirdembodiment, an on-off valve 59 b can be provided in the waste heat line59 a for circulating the heat medium 108. When the on-off valve 59 b isopened, the heat medium 108 is circulated, thereby performing heatexchange between the heat medium 108 and the combustion air 102. On theother hand, when the on-off valve 59 b is closed, the heat medium 108 isnot circulated, and thus the heat medium 108 is not heat-exchanged withthe combustion air 102.

According to the CO₂ recovery unit 53, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount in the air preheater 59 can be adjusted byoperating the on-off valve 59 b. Accordingly, a stable operation can beperformed even at the time of the load variation.

The CO₂ recovery method according to the third embodiment includes theair preheating step of preheating the combustion air 102 before reachingthe combustion facility 50 by waste heat discharged in the process ofrecovering CO₂.

According to the CO₂ recovery method, the combustion air 102 ispreheated by using waste heat discharged in the process of recoveringCO₂. Therefore, the temperature of the flue gas 101 discharged from theboiler in the combustion facility 50 rises, thereby increasing the heatexchange amount in the condensed water/flue gas heat exchanger 57. As aresult, the temperature of the condensed water 106 a returned from theregenerating heater 32 to the combustion facility 50 rises, therebyenabling to reduce consumption energy in the combustion facility 50required for recovering CO₂, and to improve energy efficiency in theplant 5 in which the CO₂ recovery unit 53 is applied.

As shown in FIG. 6, the CO₂ recovery method according to the thirdembodiment further includes a non-heat exchanging step of stopping theheat exchange at the air preheating step by closing the on-off valve 59b.

According to the CO₂ recovery method, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount at the air preheating step can be adjusted byoperating the on-off valve 59 b. Accordingly, a stable operation can beperformed even at the time of the load variation.

In FIG. 6, which explains the present embodiment, a configurationincluding the air preheater 59 (air preheating step) is shown withrespect to the configuration shown in FIG. 3, which explains the firstembodiment. However, the air preheater 59 (air preheating step) can beprovided in the configuration shown in FIG. 1, which explains the firstembodiment.

Furthermore, the configuration of the present embodiment can be aconfiguration included in the second embodiment.

Fourth Embodiment

A fourth embodiment of the present invention is explained with referenceto the drawings. FIG. 7 is a schematic diagram of a plant in which a CO₂recovery unit according to the fourth embodiment is applied.

The CO₂ recovery unit 53 according to the present embodiment includesthe condensed water/flue gas heat exchanger 57 (in a CO₂ recoverymethod, condensed water/flue gas heat exchanging step), similarly to theCO₂ recovery unit 53 according to the first embodiment. The CO₂ recoveryunit 53 further includes an air preheater 60 (in the CO₂ recoverymethod, air preheating step). Therefore, in the fourth embodiment, aconfiguration of the air preheater 60 (in the CO₂ recovery method, airpreheating step) is explained, and elements equivalent to those in thefirst embodiment described above are denoted by like reference signs andexplanations thereof will be omitted.

As shown in FIG. 7, the air preheater 60 has a condensedwater/combustion air heat exchanging line 60 a. The condensedwater/combustion air heat exchanging line 60 a is placed in thecondensed water line 32 c, and extended to the air line 56 in anupstream of air of the air/flue gas heat exchanger 55, so that thecombustion air 102 in the air line 56 is preheated by heat-exchanging itwith the condensed water 106 a to be returned from the regeneratingheater 32 to the combustion facility 50. Furthermore, the condensedwater/flue gas heat exchanger 57 is formed in the condensed water line32 c passing through the air preheater 60.

As described above, the CO₂ recovery unit 53 according to the fourthembodiment includes the air preheater 60 that preheats the combustionair 102 before reaching the combustion facility 50 by the condensedwater 106 a before reaching the condensed water/flue gas heat exchanger57.

According to the CO₂ recovery unit 53, the combustion air 102 ispreheated by using the condensed water 106 a before reaching thecondensed water/flue gas heat exchanger 57. Therefore, the temperatureof the flue gas 101 discharged from the boiler in the combustionfacility 50 rises, thereby increasing the heat exchange amount in thecondensed water/flue gas heat exchanger 57. As a result, the temperatureof the condensed water 106 a returned from the regenerating heater 32 tothe combustion facility 50 increases, thereby enabling to reduceconsumption energy in the combustion facility 50 required for recoveringCO₂, and to improve energy efficiency in the plant 5 in which the CO₂recovery unit 53 is applied.

In the CO₂ recovery unit 53 according to the fourth embodiment, a bypassline 60 b that directly connects the condensed water line 32 c withoutvia the condensed water/combustion air heat exchanging line 60 a isprovided in the condensed water line 32 c for returning the condensedwater 106 a from the regenerating heater 32 to the combustion facility50. Furthermore, an on-off valve 60 c is provided on a downstream sideof the condensed water/combustion air heat exchanging line 60 a forfeeding the condensed water 106 a to the air preheater 60. Further, anon-off valve 60 d is provided in the bypass line 60 b.

When heat exchange between the condensed water 106 a and the combustionair 102 is to be performed by the air preheater 60, the on-off valve 60c is opened and the on-off valve 60 d is closed. With thisconfiguration, the condensed water 106 a in the process of beingreturned to the combustion facility 50 via the condensed water line 32 cpasses through the condensed water/combustion air heat exchanging line60 a. Therefore, heat exchange between the condensed water 106 a and thecombustion air 102 is performed in the air preheater 60.

On the other hand, when heat exchange between the condensed water 106 aand the combustion air 102 is not performed in the air preheater 60, theon-off valve 60 c is closed, and the on-off valve 60 d is opened. Withthis configuration, the condensed water 106 a in the process of beingreturned to the combustion facility 50 via the condensed water line 32 cis returned to the combustion facility 50 without via the condensedwater/combustion air heat exchanging line 60 a. Therefore, heat exchangebetween the condensed water 106 a and the combustion air 102 is notperformed in the air preheater 60 (non-heat exchanging step).

As described above, in the CO₂ recovery unit 53 according to the fourthembodiment, the condensed water/combustion air heat exchanging line 60 afor performing heat exchange between the condensed water 106 a and thecombustion air 102 is provided in the middle of the condensed water line32 c for returning the condensed water 106 a from the regeneratingheater 32 to the combustion facility 50, and the bypass line 60 b fordirectly connecting the condensed water line 32 c without via thecondensed water/combustion air heat exchanging line 60 a is provided.

According to the CO₂ recovery unit 53, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount between the condensed water 106 a and thecombustion air 102 in the air preheater 60 can be adjusted by the bypassline 60 b. Accordingly, a stable operation can be performed even at thetime of the load variation.

The CO₂ recovery method according to the fourth embodiment includes theair preheating step of preheating the combustion air 102 before reachingthe combustion facility 50 by the condensed water 106 a, beforeperforming the condensed water/flue gas heat exchanging step.

According to the CO₂ recovery method, the combustion air 102 ispreheated by using the condensed water 106 a before reaching thecondensed water/flue gas heat exchanging step. Therefore, thetemperature of the flue gas 101 discharged from the boiler in thecombustion facility 50 rises, thereby increasing the heat exchangeamount in the condensed water/flue gas heat exchanger 57. As a result,the temperature of the condensed water 106 a returned from theregenerating heater 32 to the combustion facility 50 rises, therebyenabling to reduce consumption energy in the combustion facility 50required for recovering CO₂, and to improve energy efficiency in theplant 5 in which the CO₂ recovery unit 53 is applied.

The CO₂ recovery method according to the fourth embodiment includes thenon-heat exchanging step of returning the condensed water 106 a to thecombustion facility 50 without via the air preheating step.

According to the CO₂ recovery method, for example, when there is a loadvariation in at least one of the plant 5 and the CO₂ recovery unit 53,the heat exchange amount between the condensed water 106 a and the fluegas 101 at the condensed water/flue gas heat exchanging step can beadjusted by the non-heat exchanging step. Accordingly, a stableoperation can be performed even at the time of the load variation.

In FIG. 7, which explains the present embodiment, a configurationincluding the air preheater 60 (air preheating step) is shown withrespect to the configuration shown in FIG. 3, which explains the firstembodiment. However, the air preheater 60 (air preheating step) can beprovided in the configuration shown in FIG. 1, which explains the firstembodiment.

Furthermore, the configuration of the present embodiment can be aconfiguration included in the second embodiment.

EXAMPLES

Examples showing effects of the present invention are explained below,while the present invention is not limited thereto. FIG. 8 depicts apower output reduction rate of a process in which the method of thepresent invention is applied to a coal-combustion thermal powergenerating facility with a generating capacity of 900 megawatts.

As a comparative example, a conventional technique in which anycondensed water/flue gas heat exchanger is not provided and condensedwater is directly returned to a combustion facility is exemplified as acomparative example 1. An Example 1 has the configuration of the firstembodiment shown in FIGS. 1 to 3. An Example 2 has the configuration ofthe second embodiment shown in FIGS. 4 and 5. An Example 3 has theconfiguration of the third embodiment shown in FIG. 6. An Example 4 hasthe configuration of the fourth embodiment shown in FIG. 7.

Positions at an outlet of the CO₂ recovery unit (1), a condensed wateroutlet of the air preheater (9), a condensed water inlet of thecombustion facility (2), a flue gas inlet of the air preheater (10), anair inlet of the air/flue gas heat exchanger (3), an air inlet of thecombustion facility (4), a flue gas outlet of the combustion facility(5), a flue gas inlet of the condensed water/flue gas heat exchanger(6), a flue gas outlet of the condensed water/flue gas heat exchanger(7), and a flue gas outlet of the circulating water/flue gas heatexchanger (8) shown in FIG. 8 are indicated by like numbers in bracketsin FIG. 1, FIG. 3, FIG. 4, FIG. 6, and FIG. 7 corresponding to each ofthe Examples.

Because the comparative example 1 does not include the condensedwater/flue gas heat exchanger, the condensed water temperature at theoutlet of the CO₂ recovery unit (1) and that at the condensed waterinlet of the combustion facility (2) are both 100 [° C.], and thereforethe power output becomes 791 [MW]. The reduction in the power output inthe comparative example 1 is 12.1%.

On the other hand, because the Example 1 includes the condensedwater/flue gas heat exchanger 57, the condensed water temperature at thecondensed water inlet of the combustion facility (2) is heated to 126 [°C.] with respect to the condensed water temperature 100 [° C.] at theoutlet of the CO₂ recovery unit (1). Accordingly, the reduction in thepower output was smaller than that in the comparative example 1, and was11.6%.

The Example 2 includes the circulating water/flue gas heat exchanger 58a and the circulating water/absorbent heat exchanger 58 b, in additionto the condensed water/flue gas heat exchanger 57. Therefore, thecondensed water temperature at the condensed water inlet of thecombustion facility (2) was heated to 126 [° C.] with respect to thecondensed water temperature 100 [° C.] at the outlet of the CO₂ recoveryunit (1), and the rich solution 104 b of the absorbent 104 was heated to93.8 [° C.] by the circulating water/flue gas heat exchanger 58 a andthe circulating water/absorbent heat exchanger 58 b. Accordingly, thereduction in the power output was smaller than that in the comparativeexample 1, and was 11.3%.

The Example 3 includes the air preheater 59 according to the thirdembodiment shown in FIG. 6, in addition to the condensed water/flue gasheat exchanger 57. Therefore, the condensed water temperature at thecondensed water inlet of the combustion facility (2) was heated to 154[° C.] with respect to the condensed water temperature 100 [° C.] at theoutlet of the CO₂ recovery unit (1). Accordingly, the reduction in thepower output was smaller than that in the comparative example 1, and was10.8%.

The Example 4 includes the air preheater 60 according to the fourthembodiment shown in FIG. 7, in addition to the condensed water/flue gasheat exchanger 57. Therefore, the condensed water temperature at thecondensed water inlet of the combustion facility (2) was heated to 157[° C.] with respect to the condensed water temperature 100 [° C.] at theoutlet of the CO₂ recovery unit (1). Accordingly, the reduction in thepower output was smaller than that in the comparative example 1, and was10.8%.

As a result, as shown in FIG. 8, according to these Examples, it can beunderstood that energy efficiency in the combustion facility can beimproved because the power output is improved.

REFERENCE SIGNS LIST

-   -   1 cooling column    -   1 e cooler    -   2 absorber    -   22 f cooler    -   3 regenerator    -   31 absorbent regenerating unit    -   31 e cooler    -   32 regenerating heater    -   32 a heating line    -   32 b steam extracting line    -   32 c condensed water line    -   33 CO₂ recovering unit    -   33 b cooler    -   34 lean solution/condensed water heat recovery unit    -   4 rich/lean heat exchanger    -   5 plant    -   50 combustion facility    -   51 flue gas duct    -   52 desulfurizer    -   53 CO₂ recovery unit    -   54 stack    -   55 air/flue gas heat exchanger    -   56 air line    -   57 condensed water/flue gas heat exchanger    -   58 a circulating water/flue gas heat exchanger    -   58 b circulating water/absorbent heat exchanger    -   59 air preheater    -   60 air preheater    -   101 flue gas    -   101 a emission gas    -   102 combustion air    -   103 cooling water    -   104 absorbent    -   104 a lean solution    -   104 b rich solution    -   105 wash water    -   106 steam    -   106 a condensed water    -   107 circulating water    -   108 heat medium

1. An operation method of a plant comprising: a combustion step thatdischarges flue gas to a flue gas duct and heats condensed water from acondensed water line so as to discharge the heated condensed water to asteam extracting line as steam; an air/flue gas heat exchanging stepthat heat-exchanges the flue gas with combustion air; a CO2 recoverystep including: an absorbing step that reduces CO₂ in flue gasdischarged from the combustion step via the air/flue gas heat exchangingstep by absorbing CO₂ by an absorbent; a regeneration step that heatsthe absorbent having absorbed CO₂ to emit CO₂, and regenerates andsupplies the absorbent to the absorbing step; and a regenerating heatstep that heats the absorbent in the regeneration step with the steamfrom the steam extracting line and returns heated condensed water to thecombustion step via the condensed water line; and a condensed water/fluegas heat exchanging step that heats the condensed water of the condensedwater line by heat-exchanging the condensed water with the flue gas inthe flue gas duct discharged from the air/flue gas heat exchanging step.2. The method according to claim 1, further comprising: a bypass step ofdirectly supplying the condensed water of the condensed water linewithout via the condensed water/flue gas heat exchanging step.
 3. Themethod according to claim 1, further comprising: a circulatingwater/flue gas heat exchanging step that performs heat exchange betweencirculating water and the flue gas in the flue gas duct after thecondensed water/flue gas heat exchanging step; and a circulatingwater/absorbent heat exchanging step that performs heat exchange betweenthe absorbent having absorbed CO₂ in the absorbing step and thecirculating water before the absorbent reaches the regeneration step. 4.The method according to claim 1, further comprising an air preheatingstep that preheats the combustion air before the combustion step bywaste heat discharged in a process of CO₂ recovery step.
 5. The methodaccording to claim 1, further comprising an air preheater that preheatsthe combustion air before reaching the combustion step by the condensedwater before reaching the condensed water/flue gas heat exchanging step.